Re: Combined VIC and PET cartridge

From: Marko Mäkelä (
Date: 2001-05-21 15:06:05

On Mon, 21 May 2001, Ruud Baltissen wrote:

> So IMHO you have two solutions:
> - you use $9xxx and/or $Axxx
> - you use $E9xx..$EFFF (if available), but complete decoding needed

So, the I/O area may be a bit problematic, since I'm feeding only one CPU
address line to the logic array.

> Seen from the CPU, the 6545 only uses two registers. So the fact that the
> INTERNAL registeres R18/31 are used or not, doesn't matter.

It does matter if I build a finite state machine that latches the 6545
register selection commands and then intercept writes to, say, R31 (or
also R30).  The 6545 document on FUNET says that when R31 is read, the
data bus will not be driven.  But I don't know of other registers.  Time
to write a test program, I guess.  I was also surprised that according to
the schematic diagram, the hardware cursor of the 6545 is not used.

The TA12 output of the 6545 (8032081 sheet 8 of 11) is labelled "invert".
When the text matrix is moved to $1000, will all characters be reversed?  
Could this be used for fancy raster effects? How accurate is the "vertical
blank" bit? Are there any advanced graphics demos for the PET?


This message was sent through the cbm-hackers mailing list.
To unsubscribe: echo unsubscribe | mail

Archive generated by hypermail 2.1.1.